1. Field of the Invention
The present invention relates to dielectric ceramic compositions for use as resonators employed in a microwave frequency band of several gigahertz.
2. Description of the Prior Art
In recent years, attempts to use a dielectric material for a resonator or a filter have been made in satellite communication, broadcasting and microwave remote communication using a microwave having a frequency of several gigahertz or a transmitter-receiver such as a microwave remote recognition system.
Examples of this type of dielectric ceramic material conventionally used include a composition of a BaO-TiO.sub.2 -Nd.sub.2 O.sub.3 -Bi.sub.2 O.sub.3 system which is proposed in, for example, Japanese Patent Laid-Open Gazette No. 8806/1986.
In this conventional dielectric ceramic composition, however, its dielectric constant .epsilon. is as large as 70 to 90, but its Q value is as small as a maximum of approximately 4700 at 1 GHz. In addition, the temperature coefficient of resonance frequency .tau.f of the dielectric ceramic composition is also slightly as large as +10.about.+20 PPM/.degree.C., so that sufficient properties cannot be obtained.
However, when the frequency band to be used is as high as several gigahertz, a material having a large Q value is required. For example, in a dielectric filter using a material having a high Q value, lines are easily coupled to each other so that the resonance peak is sharp, which is preferable. Consequently, a dielectric material having a high Q value is desired.
Furthermore, there are compositions of a TiO.sub.2 -ZrO.sub.2 -SnO.sub.2 system which are proposed in, for example, Japanese Patent Laid-Open Gazette Nos. 192460/1990, 29009/1987, 29010/1987 and U.S. Pat. Nos. 4,339,543, 4,665,041 and 4,785,375.
In the compositions of a TiO.sub.2 -ZrO.sub.2 -SnO.sub.2 system, their Q values are as high as a maximum of approximately 9000 at 7 GHz.
The inventors of the present application have examined the compositions of a TiO.sub.2 -ZrO.sub.2 -SnO.sub.2 system from various points of view so as to provide a microwave dielectric ceramic composition having new composition which has a large dielectric constant and has a high Q value.